MASSAPEQUA PARK, N.Y. (AP) — Investigators have been digging in the yard at the Long Island home of Rex Heuermann, who was charged earlier this month with killing at least three women and burying their remains on a remote stretch of beach highway.

On Sunday, a yellow excavator was seen scooping dirt in the alleged killer’s backyard, according to aerial footage shared by News 12. Investigators could be seen scraping through the freshly upturned earth with shovels. The digging equipment was still on the scene Monday morning.

A neighbor told the Associated Press said he witnessed men who appeared to be police lifting the front porch of the house on Sunday afternoon.

“They yelled ‘lift’ and brought it up in one big piece, as if it was a cover,” Barry Auslander said.

The porch has been replaced by a white tent, with a state medical examiner’s truck parked nearby.

Investigators are trying to determine whether any of the killings happened inside the Massapequa Park home that Heuermann shared with his wife and two children.

Authorites have pulled more than 100 firearms from the house, along with a large doll encased in glass and a portrait of a woman with a bruise on her face. Police also got a warrant to conduct searches of Heuermann’s property in South Carolina.

The July 14th arrest of Heuermann, a 59-year-old architect, marked a stunning breakthrough in the long-stalled cold case that first drew headlines in 2010, when police began searching for a missing woman, Shannon Gilbert, near Long Island’s Gilgo Beach.

Instead, they discovered 10 sets of human remains scattered along a long barrier island. The dead included eight women, one man and a young child.

Heuermann, who has pleaded not guilty, was charged with killing three of the women – Melissa Barthelemy, Amber Costello, and Megan Waterman. He is the prime suspect in the death of a fourth woman, Maureen Brainard-Barnes.

The bodies of the four women were found along the same quarter-mile (0.4-kilometer) stretch of Ocean Parkway. Heuermann has not been accused in connection to the other remains, and police have suggested the deaths may be the work of multiple killers.

In South Carolina, where Heuermann’s brother lives, police are seeking video recordings and writings related to the killings, burlap, duct tape, guns and ammunition, cutting tools, and a specific type of paper towel from the Bounty Modern Print Collection.

Authorities also seized a Chevrolet Avalanche, which Heuermann had transferred to his brother in 2012, from the property. The vehicle was spotted by a roommate of one of the victims shortly before her disappearance, a tip that ultimately proved crucial in helping police make an arrest.